This invention relates to image reproduction systems and more particularly to image reproduction systems involving the application of toner particles over a tacky surface to develop a latent image.
2. Description of the Prior Art
The advent of electrophotography and wide acceptance of the electrostatic reproduction method have resulted in a large number of processes and devices useful in the application of toner particles on an electrically charged surface. Mechanisms and associated methods such as cloud chambers, cascade developers, transfer brushes, and rollers are well known. In general, some means are usually provided to meter the amount and/or rate of toner application.
In the graphic arts area, a system of image reproduction has been employed, whereby a photosensitive element is first exposed to actinic radiation in an imagewise exposure. The element exhibits a different degree of tackiness as a result of this exposure. The latent image can be developed through a process called toning, whereby toner particles are distributed over the surface of the element and adhered to the tacky areas. A typical such element and associated process, capable of producing multi-colored images is described in V. F. H. Chu et al, U.S. Pat. No. 3,649,268 and the patents referred to therein, while a description of a typical toning method is found in M. Burg et al, U.S. Pat. No. 3,060,024.
It has also been known in the art to use a small pad having a handle on one side and a thick pile, such as lambswool, on the other, to apply and distribute the toner over the latent image-bearing surface. The pad is dipped in a dish containing a supply of toner; it is then rubbed lightly and repeatedly in an S-type path over the latent image-bearing surface. Toner particles adhere to the tacky areas and the image is thus developed.
Another practice has been to first apply the toner by patting a pad dipped in toner all over the surface and then using it to rub the surface with an S-type motion as before. This practice is slow, untidy, and generates an objectionable dust cloud during the patting operation. Results generally lack reproducibility.
Rotating, or combinations of rotating and oscillating cylindrical brushes used to embed a toner in the soft areas of an imagewise exposed surface have also been tried in the prior art, and a good summary of the various alternatives will be found in R. W. Jones et al, U.S. Pat. No. 3,723,123.
Both electrostatic and tacky surface image development involve the application of toner particles over a latent image-bearing surface. In that respect there is a similarity in the problems encountered, especially the problems relating to the dispensing of toner particles. However, systems using the tacky surface principle, be it a situation where the toner particles simply adhere to the surface or are embedded therein, present an additional problem. The amount of toner adhered to the tacky surface tends to vary, depending on the delivery rate and method or distribution over the surface. This is particularly noticeable where the toning step is done manually, resulting in nonreproducible development. Additionally, the softer, tacky surface is vulnerable to scratching.
In an effort to eliminate these problems, the patting method and roller applicators have been introduced, but with questionable results. Problems still unsolved are uniformity of density over large, said color areas, dust clouds, reproducibility and ease of handling.
A need for a simple and reliable method to reproducibly distribute toner over a tacky surface still persists.